Fundamental ion cyclotron resonance heating of JET deuterium plasmas

Abstract

Radio frequency heating of majority ions is of prime importance for understanding the basic role of auxiliary heating in the activated D-T phase of ITER. Majority Deuterium Ion-Cyclotron Resonance Heating (ICRH) experiments at the fundamental cyclotron frequency were performed in JET. In spite of the poor antenna coupling at the lowest possible commissioned RF frequency (25MHz), this heating scheme proved promising when adopted in combination with D Neutral Beam Injection (NBI). The experiments were performed in a ~90% D, 5% H plasma with some pulses including traces of Be and Ar. Up to 2MW of ICRH power was applied with dipole phasing in conjunction tõ 6MW of NBI power, either using 80keV "normal" beam or 130keV "tangential" beam injection. The toroidal magnetic field strength was typically B 0 = 3.3T, providing core ICRH of the bulk D ions. The effect of fundamental D ICRH was clearly demonstrated in these experiments: By adding 25% of heating power (P ICRH = 1.7MW / P NBI+OH = 7MW) the fusion power was increased up to 30-50%, depending on the type of NBI adopted. At this power level, the ion and electron temperatures increased from T i ~ 4.0keV and T e ~ 4.5keV (NBI-only phase) to T i ~ 5.5keV and T e ~ 5.2keV (ICRH+NBI phase), respectively. The increase in the neutron yield was stronger when 80keV rather than 130keV Deuterons were injected in the plasma. It is shown that the neutron rate, the diamagnetic energy and the electron as well as ion temperature scale roughly linearly with the applied RF power. A synergistic effect of the combined use of ICRF and NBI heating was observed: (i) The number of neutron counts measured by the neutron camera during the combined ICRF+NBI phases of the discharges exceeded the sum of the individual counts of the NBI-only and ICRF-only phases; (ii) A substantial increase in the number of slowing-down beam ions was detected by the TOFOR spectrometer when ICRF power was switched-on; (iii) A small D subpopulation with energies slightly above the NBI launch energy were detected by the neutral particle analyzer and gray spectroscopy.

Global anomalous transport of ICRH- and NBI-heated fast ions

“…It has been experimentally observed that simultaneously applying NBI and IRCH heating simultaneously results in more heating than the sum of either of them alone [18]. Our results provide a possible explanation for this phenomenon.…”

Synergetic heating of D-NBI ions in the vicinity of the mode conversion layer in H-D plasmas in JET with the ITER like wall.

“…Indeed, D and 4 He ions have the same (Z/A) = 1/2 and thus there is no MC layer in the plasma and no local amplification of the E + field. In fact, pulse #55714 is very similar to the discharges studied in [10,11], and highlights that fundamental ICRH heating of beam ions can be made significantly much more efficient in plasmas with a purposely chosen particle composition. [14]).…”

“…Note that the Doppler-shifted ion cyclotron absorption by D-beam ions in D plasmas was earlier reported on JET [10,11]. In those experiments there was no MC layer present in the plasma, and the double-pass absorption was computed to be 5-15% [11].…”

First neutron spectrometry measurements in the ASDEX Upgrade tokamak

“…One of the most interesting applications of the CNS to ASDEX Upgrade plasmas is the investigation of the synergy effect between NBI and the Ion Cyclotron Resonance Heating [13,14]. It is a common observation in tokamaks that adding radio-frequency heating on top of NBI enhances the neutron rate by more than the rate associated with ICRH only under the same experimental conditions and plasma parameters [15]. An example for an ASDEX Upgrade discharge is shown in figure 8.…”